1. Field of the Invention
The present invention relates generally to semiconductor packages, and more particularly to a semiconductor package having reduced inductance, and a method of manufacturing such semiconductor package.
2. Description of the Related Art
Semiconductor dies are conventionally enclosed in plastic packages that provide protection from hostile environments and enable electrical interconnection between the semiconductor die and an underlying substrate such as a printed circuit board (PCB) or motherboard. The elements of such a package include a metal leadframe, an integrated circuit or semiconductor die, bonding material to attach the semiconductor die to the leadframe, bond wires which electrically connect pads or terminals on the semiconductor die to individual leads of the leadframe, and a hard plastic encapsulant material which covers the other components and forms the exterior of the semiconductor package commonly referred to as the package body.
The leadframe is the central supporting structure of a semiconductor package. In many semiconductor package designs, that portion of the leadframe to which the semiconductor die is bonded effectively functions as and is commonly referred to as a heat sink. In most semiconductor package configurations, a portion of the leadframe is internal to the package, (i.e., completely surrounded by the package body). Portions of the leads of the leadframe typically extend externally from the package body or are partially exposed therein for use in electrically connecting the package to another component. Similarly, at least a portion of the heat sink is exposed in the package body to discharge heat generated by the semiconductor die. The heat sink of the leadframe is also often referred to as a die pad.
In the electronics industry, there is continued development of semiconductor dies which have increasing processing speeds and higher degrees of integration. For a semiconductor package to accommodate these enhanced semiconductor dies, the number of leads included in the semiconductor package must be significantly increased. To avoid an undesirable increase in the size of the semiconductor package attributable to the increased number of leads, a common practice is to reduce or narrow the lead pitch. However, a result of the narrowing of the lead pitch is an increase in the level of self inductance and mutual inductance (hereinafter collectively referred to as “inductance”) generated from the leads of the semiconductor package. Thus, leadframe type semiconductor packages are typically considered to be unsuitable for semiconductor dies which transmit signals at high speed since the relatively high inductance of such semiconductor packages may distort the signals transmitted from such high speed semiconductor dies. In this regard, many mobile communication devices (e.g., cellular phones) and personal communication devices which are equipped with semiconductor dies capable of transmitting high-frequency signals typically are outfitted with BGA (ball grid array) semiconductor packages which accommodate such semiconductor dies. If such semiconductor dies were to be installed or packaged in a leadframe type semiconductor package, significant signal loss may be created due to the inductance problem described above.
In recognition of this problem and the need to change the structure of leadframe type semiconductor packages to accommodate semiconductor dies which transmit signals at high speeds, there has been developed in the prior art a leadframe type semiconductor package wherein a semiconductor die and a ground lead are each bonded to a heat sink or die pad through the use of conductive wires, thereby reducing inductance with respect to the ground lead. However, the effective reduction in inductance achieved in this type of semiconductor package is not significant since only a narrow area of the heat sink or die pad bonded to the conductive wire acts a ground, with the remaining area of the heat sink or die pad not acting as a ground. These deficiencies are addressed and overcome by the semiconductor package constructed in accordance with the present invention, as will be described in more detail below.